Production of acrylic composite fibers

ABSTRACT

AN IMPROVEMENT IN PRODUCTION OF ACRYLIC CONJUGATE FIBERS HAVING LATENT THREE-DIMENSIONAL COIL CRIMPS, WHICH IMPROVEMENT CONCERNS (1) UTILIZING A HIGH SHRINKING POLYMER COMPONENT CONTAINING 85-94% ACRYLONITRILE AND A LOW SHRINKING COMPONENT CONTAINING A GREATER AMOUNT OF ACRYLONITRILE THAN THE HIGH SHRINKING COMPONENT, (2) HEAT-TREATING THE FILAMENTS IN A RELAXED STATE AT 105140*C WHILE MAINTAINING A MOISTURE CONTENT OF MORE THAN 150% AND (3) PULLING THE FILAMENTS OUT OF SAID TREATMENT UNDER SPECIFIC TEMPERATURE AND TENSION CONDITIONS.

7, 1974 KEITARO SHIMODA ETAL 3,809,738

PRODUCTION OF ACRYLIC COMPOSITE FIBERS Original Filed Nov. 25, 1969 3 Sheets-Sheet 1 m (f "S (D m m Strain 2 m0 H m m (D A a P 3 l0 v Acrylonitrile content y 7, 1974 KEITARO SHIMODA ETAL 3,809,738

PRODUCTION OF ACRYLIC COMPOSITE FIBERS Original Filed Nov 25, 1969 3 Sheets-Sheet 2 (p/3111) ssezas Pulling-out temperature g y 1974 KEITARO SHIMODA ETAL 3,809,738

PRODUCTION OF ACRYLIC COMPOSITE FIBERS Original Filed Nov 25. 1969 3 Sheets-Sheet 5 l 11 J a 1 1 F I 1 United States Patent 3,809,738 PRODUCTION OF ACRYLIC COMPOSITE FIBERS Keitaro Shimoda, Yutaka Kobayashi, and- Takehiko Sumi, Okayama, Japan, assiguors to Japan Exlan Company, Limited, Osaka, Japan Continuation of application Ser. No. 879,828, Nov. 25, 1969. This application Dec. 5, 1972, Ser. No. 312,355 Claims priority, application Japan, Nov. 26, 1968, 43/ 86,839 Int. Cl. D01d /22 US. Cl. 264-168 2 Claims ABSTRACT OF THE DISCLOSURE An improvement in production of acrylic conjugate fibers having latent three-dimensional coilcrimps, which improvement concerns (1) utilizing a high shrinking polymer component containing 85-94% acrylonitrile and a low shrinking component containing a greater amount of acrylonitrile than the high shrinking component, (2) heat-treating the filaments in a relaxed state at 105- 140 C. while maintaining a moisture content of more than 150% and (3) pulling the filaments out of said treatment under specific temperature and tension conditions.

This is a continuation of application Ser. No. 879,828, filed Nov. 25, 1969 now abandoned.

This invention relates to an improvement in production of acrylic conjugate fibers having latent three-dimensional coil crimps.

It is Well known that conjugate fibers (sometimes called composite fibers), made by arranging at least two kinds of fiber forming components (polymers) having different thermoshrinking behaviors eccentrically or laminarly along the entire length in the axial direction of the fiber, are used extensively due to their remarkable bulkiness and elasticity. Their use is based on the development of three-dimensional coil crimps due to the difference in thermal shrinkage of the components constituting the fiber. However, it is also known that, in the case where excess coil crimps are developed in the conjugate fibers, it becomes difiicult to handle them in the subsequent yarn forming step or knitted fabric producing step.

For example, when conjugate fibers, in which coil crimps exceeding a desirable range have been developed, are to be carded with a carding machine, a phenomenon of the fibers to be wound on the cylinder or doifer will often occur which not only makes the carding operation ditficult but also causes the formation of a large amount of neps in the carded Web, and thus creates problems which can not be overlooked when the object is to im-,

prove the fiber quality. Further, it is well known that a yarn made of such conjugate fibers will lose a part of its three-dimensional coil crimps and will impair the bulkiness or dimensional stability during the spinning (yarn forming) step or knitting or weaving preparation step.

In order to overcome these difficulties, there have been suggested, for example, (1) a method wherein the development of three-dimensional coil crimps in the production of conjugate fibers is inhibited, and after a yarn or knitted or woven fabric has been formed it is then heat-treated so that coil crimps may be well developed, and (2) a method wherein conjugate fibers in which coil crimps have been developed in the fiber production step are restretched or tensioned so that the crimps are rendered latent in the fiber materials. As the method 1, more particularly, there is known a method wherein two kinds of thermoplastic substances different in shrinking temperature are simultaneously extruded from a common orifice to form a filament, which is then stretched and 3,809,738 Patented May 7, 1974 made nonplastic by drying or the like while maintaining the filament in a tensioned state (US. Pat. No. 2,439,815). As methods belonging to Group 2, there can be enumerated, for example, those mentioned in British Pat. Nos. 1,027,018 and 1,044,471. Thus in British Pat. No. 1,027,018, there is suggested a method wherein two or more kinds of polymers different in thermal shrinkage and each consisting mainly of acrylonitrile are compositely extruded through a common orifice to form a composite fiber, which is stretched and collapsed and then restretched under certain temperature conditions.

However, in the first method 1, there is a disadvantage in that the deformation of the crystal structure produced within the fiber with the stretching will not be substantially removed in the fiber producing step and therefore it can not in fact be expected to obtain acrylic conjugate fibers having a favorable fiber quality.

Further, in the second method 2, the restretching or tensioning treatment designed to impart latent threedimensional coil crimps to the acrylic conjugate fibers is carried out in a different or separate step from the relaxing step, and therefore it is necessary to provide a special stretching apparatus (e.g. turbostapler or Pacific converter) and hence the process is complicated. Further, the thus obtained acrylic conjugate fibers have a residual shrinkability, and therefore the dimensional stability of the product, such as yarn or knitted or woven fabric, made from these fiber materials will be impaired. Particularly, when the temperature in the tensioning or restretching step is higher than C., not only will a considerable restriction have to be applied to the treating conditions in the subsequent steps including the dyeing step, but also the subsequent development of three-dimensional coil crimps will become nonuniform and the reduction of the dimensional stability based on the residual shrinkage Will be remarkable.

Therefore, it is an object of this invention to provide a process for producing acrylic conjugate fibers having latent three-dimensional coil crimps but substantially no residual shrinkability.

Another object of the present invention is to combine a heat-relaxing treatment step and filament pulling-out step in a process for producing acrylic conjugate fibers so that the process may be shortened and simplified and a desirable latent crimpability imparted to the acrylic conjugate fibers without adopting a restretching step at a temperature above 100 C.

A further but different object of the present invention is to find desirable tension and temperature conditions to be applied to acrylic conjugate fibers in the step of pulling them out.

Further objects of the present invention will become clear from the following description.

It has now been found that the residual shrinkability of acrylic conjugate fibers having latent crimpability will be remarkably influenced by the magnitude of the tension and the heating temperature applied to a filament when the filament is pulled out of the heat-relaxing treatment step, and that the magnitude of said tension can be rep resented by the correlation between the acrylonitrile content in the high shrinking component forming the acrylic conjugate fibers and the temperature of pulling out the filament after the heat-relaxing treatment.

It has also been found that, in order to remove threedimensional coil crimps of acrylic conjugate fibers heattreated in a relaxed state and to render the coil crimps latent, it is necessary to apply to the heat-relaxing treated fibers a tension required to leave some of the three-dimensional coil crimps of the acrylic conjugate fibers or to keep the fibers almost straight. It has been found that the value of this tension should be determined so that no substantial stretching action is given to the acrylic conjugate fibers having passed through the heat-relaxing treatment step. Such tension to be applied according to this invention is referred to as uncrimping force which will be defined later.

FIG. 1 is a stress-strain diagram defining the unreference to the accompanying drawings wherein:

FIG. 1 is a stress-strain diagram defiining the uncrimping force of the present invention;

FIG. 2 is a diagram showing the relation between the acrylonitrile content and uncrimping force in the high shrinking component of an acrylic conjugate fiber;

FIG. 3 is a diagram showing the relation between the treating temperature to erase the coil crimps of an acrylic conjugate fiber and the uncrimping force; and

FIG. 4 is a vertically sectioned view of an apparatus to be used to carry out the process of the present invention.

FIG. 1 illustrates the definition of uncrimping force. There is shown a stress-strain diagram of acrylic conjugate fibers having coil crimps, the straight line part of the diagram showing that the coil step substantially vanishes, which is the part of the diagram in which Hooks proportional law is considered to hold between the substantial elongation produced in the acrylic conjugate fiber and the tensile stress produced in the crosssection of the fiber. The straight line is extended downward, and an intersection A of said extended line with the curved portion of the line extending from the original point of the stress-strain diagram is determined. The value F (mg./d.) of the tensile stress corresponding to the point A is defined as the uncrimping force. According to applicants findings, in an acrylic conjugate fiber made by joining two or more kinds of acrylonitrile polymers different in thermoshrinking behavior as fiber forming components eccentrically or laminarily along the entire length in the axial direction of the fiber, the uncrimping force depends on the acrylonitrile content in the high shrinking component containing from 85 to 94% of acrylonitrile by weight, the temperature at which the filament is pulled out after the heat-relaxing treatment and also on the monofilament denier of the acrylic conjugate fiber. Thus, only when such uncrimping force defined by these factors is applied, under the maintenance of a required temperature condition, to acrylic conjugate fibers having passed through a heat-relaxing treatment step and the filament is continuously pulled out (under the application of such uncrimping force) after the heat-relaxing treating step, can there be produced acrylic conjugate fibers having latent three-dimensional coil crimps and substantially no residual shrinkage.

FIG. 2 shows an uncrimping force in hot water at 95 C. of an acrylic conjugate fiber of a monofilament having a fineness of 3 deniers made by preparing a spinning solution in which the acrylonitrile content in the acrylonitrile polymer forming the high shrinking component of the acrylic conjugate fiber is varied within a range of from 85 to 94% by weight and a spinning solution in which the acrylonitrile content in the acrylonitrile polymer forming the low shrinking component is 2% higher than the acrylonitrile content in the high shrinking component, and compositely wet-spinning both spinning solutions to form conjugate fibers, stretching, drying and heat-relaxing treating the fibers.

FIG. 3 illustrates the relation between the uncrimping force and the filament heating temperature (represented as a reciprocal number of the absolute temperature in T K.) when pulling a filament (as prepared in the same manner as explained above for FIG. 2) out of the heat-relaxing treatment step.

It will be understood from FIGS. 2 and 3 that the uncrimping force to be applied to make three-dimensional coil crimps latent and to remove or avoid residual shrinkability will be influenced by the acrylonitrile content in the acrylic polymer forming the high shrinking component of the conjugate fiber and the temperature of pulling out the conjugate filament which has passed through the heat-relaxing step.

By repeating precise experiments on the basis of such findings as mentioned above, it has been found that, in producing acrylic conjugate fibers, if the fiber is pulled out of the heat-relaxing treatment step while a particular tension-defined by the acrylonitrile content in the high shrinking component of the conjugate fiber containing from to 94% of acrylonitrile and the temperature at which the fiber is pulled out of the heat-relaxing treatment step is being applied thereto, the objects of the present invention are attained. More particularly, the objects of the present invention can be attained by pulling out of the heat relaxing step a filament consisting of a high shrinking component having an acrylonitrile content of from 85 to 94% and a low shrinking component in which the acrylonitrile content is higher than in the high shrinking component, while applying thereto tension and temperature conditions represented by in a range of 353T372 or in a range of 333 T353 wherein F is the tension (mg/d.) under which the conjugate fibers are pulled out, AN is the acrylonitrile content (in percent) in the high shrinking component of the conjugate fibers, T is a heating temperature (in K. absolute temperature) at which the filaments are pulled out from the heat-relaxing treatment step and D is the fineness (in denier number) of the monofilament of the conjugate fibers.

The process for producing acrylic conjugate fibers according to the present invention will be explained in more detail in the following.

In preparing the spinning solution from acrylonitrile polymers, it is necessary to select respective acrylonitrile polymers having different acrylonitrile contents for the high shrinking component and low shrinking component which constitute the conjugate fiber, and to adjust the acrylonitrile content in the component having the low acrylonitrile content, that is, the high shrinking component, to within a range of from 85 to 94%. Further, for the low shrinking component, an acrylonitrile polymer in which the acrylonitrile content is higher than in the high shrinking component is utilized. In case the acrylonitrile content in the high shrinking component exceeds 94%, it will be difficult to impart sufficient coil crimpability to the resulting conjugate fibers. Further, in case the acrylonitrile content in the high shrinking component does not reach 85%, the shrinkage of the fibers in the heat-relaxing treatment step will become so excessive as to remarkably impede various working factors such as the spinnability and uniform dyeability in subsequent steps.

Further, the filament heating temperature in the step of pulling out the filaments in order to render three-dimensional coil crimps latent after the heat-relaxing treatment should be in a range of 60 to 99 C. In case the filament heating temperature in this step is below 60 C., the coil crimps developed in the heat-relaxing treatment will not be removed and will not only make it difiicult to process the yarn or knitted or woven fabric in subsequent steps but will also apply an unnecessary frictional force to the filaments in the outlet seal of the heat-relaxing apparatus and frequently damage the fibers. If the temperature of the pulling-out step exceeds 99 C., the development of the three-dimensional coil crimps in the subsequent wet-heating or dyeing step of the yarn or knitted or woven fabric will inevitably be insufiicient unless a temperature higher than that used in the pulling-out step is utilized and, as a result, not only will the processing conditions be remarkably restricted but also dimensional stability will be absent and the shape stabilizing property and hand of the product will be impaired. Further, when the filaments are pulled out while a temperature higher than 99 C. is maintained, there will be a tendency such that partial elongation is imparted to the filaments with a slight fluctuation of the pulling-out tension and the defect of imparting a partial residual shrinkage to the resulting fiber will result.

FIG. 4 illustrates a heat relaxing apparatus having an inlet sealing mechanism 12 and an outlet sealing mechanism 14. Filaments introduced through the inlet sealing mechanism 12 are guided into the main body 50 of a pressure vessel by feeding rolls 16 and 18. The filaments flow down along an inclined chute 22 together with warm water fed through a warm water inlet port 24. Then the filaments are guided onto a coarse screen conveyer 52 and moved toward the outlet part of the body 50 while being heat-treated in a relaxed state by steam introduced through inlet ports 100. During their travel, the filaments on the conveyor 52 are subjected to the action of the steam heat having a required temperature While being maintained in a nontensioned state adapted to the desired heat relaxing treatment. The filaments heat-treated in a relaxed state on the conveyer 52 are then passed through a guide rod 53, cage roll 54, guide rod 56 and tension controlling rods 58 adjustably mounted in an outlet water cylinder 66. During the upward passage through the water column 66, the filaments are subjected to a pulling-out tension (uncrimping force in the present invention) and are pulled out of the pressure vessel 10 by take-out rolls 82 and 84 through the outlet sealing mechanism 14 so that the three-dimensional coil crimps of the filaments developed on the conveyer 52 are rendered latent.

Into the outlet water cylinder 66 is fed hot Water to heat the filaments to the required temperature in pulling out the filaments, the water being fed through a conduit pipe 62 and a reservoir 64 in the vessel. A part of the hot water overflows through an overflowing port 60 of the reservoir so as to constitute a liquid 120 in the vessel 10 and the rest of the hot water is pushed up through the water cylinder 66, passed through the outlet sealing mechanism 14 and an outlet water reservoir 68 and is discharged through a conduit pipe 70.

By making the positions of the tension controlling rods 58 adjustable, it is possible to adjust the pulling-out tension so that the three-dimensional coil crimps developed in the heat-relaxing treatment step may be rendered latent. The bottom liquid 120 in the vessel 10 is drained through drain ports 72 and 74.

In carrying out the method of this invention, the acrylic composite fibers are stretched, dried and then subjected to the above heat-relaxing treatment. This heat-relaxing treatment is a step indispensable not only to develop and fix the three-dimensional coil crimps but also to improve the fiber properties, particularly the knot strength, and to prevent fibrillation. Without this step, it is impossible to obtain conjugate fibers having practically desirable crirnpability and high strength and elongation. It is desirable to carry out the heat-relaxing treatment at a temperature of 105 to 140 C. while maintaining a moisture content in the filaments of more than 150% (based on the dry fiber weight). If the water contained in the fibers is below 150%, the slip between the monofilaments will become insufiicient in that three-dimensional coil crimps will not be adequately developed. When the heatrelaxing treatment temperature is below 105 C, there is no sufiicient heat-relaxing effect. Further, if the heat-relaxing treatment temperature is above 140 0, threedimensional coil crimps will develop in excess and, even if the pulling-out tension defined by the above formula is applied, it will be difiicult to render the coil crimps latent to the desired extent, and further the whiteness of the resulting fibers will become poor.

The spinning operation (formation of composite fibers) and subsequent stretching and drying may be conducted in a well known manner. However, it is preferable to conduct the drying in a manner as disclosed in British Pat. No. 849,465. Thus, the composite filaments are dried under a specific temperature and humidity correlated condition so that the fibrillating tendency of the fibers is reduced and the dyeability, wear-resistance and strength of the fibers are improved.

As acrylonitrile polymers which can be used in the pres ent invention, there can be mentioned acrylonitrile homopolymers and acrylonitrile copolymers containing at least by weight of acrylonitrile and at least one monomer copolymerizable with acrylonitrile as the component other than acrylonitrile. Such homopolymers and copolymers may be obtained by any conventional method. As monomer compounds copolymen'zable with acrylonitrile, there can be exemplified'methyl acrylate, ethyl acrylate, butyl acrylate, methoxyethyl acrylate, phenyl acrylate, cyclohexyl acrylate, dimethylaminoethyl acrylate and corresponding esters of methacrylic acid; alkyl substituted products and nitrogen substituted products of acrylamides and methacrylamides; unsaturated ketones such as methylvinylketones, phenylvinylketone and methylisopropenylketone; vinyl carboxylates such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; esters of ethylene alpha-beta-carboxylic acids such as fumaric acid, citraconic acid, mesaconic acid and aconitic acid; N-alkyl-maleinimide; N-vinylcarbazole; N- vinylsuccinimide; N vinyl phthalimide; vinylether; N- methylolacryl amide; vinylpyridines such as 2-vinylpyridine, 4-vinylpyridine and 2-methyl-5-vinylpyridine; styrene and its alkyl substituted products; vinyl chloride; vinylidene chloride; vinylidene cyanide.

Further, as solvents which can be used to prepare the spinning solutions, there can be enumerated concentrated aqueous solutions of a thiocyanate of an alkali metal such as lithium thiocyanate, potassium thiocyanate or sodium thiocyanate or ammonium thiocyanate, concentrated aqueous solutions of an inorganic acid such as sulfuric acid or nitric acid, or organic solvents such as dimethylformamide, dimethylacetamide or dimethylsulfo xide.

Examples of the present invention will be given as follows. However, the present invention is not limited to the particular examples. The crimp frequency, crimp product and residual shrinkage referred to in the examples were measured by the below-mentioned methods. Further, except in a special case, the fiber forming component and water content are all represented in terms of percent by weight.

Crimp frequency: A load of 2 mg. per unit denier was applied to the sample to be measured and the number of crimps per 25 mm. of the length of the sample was measured. This value is defined as the crimp frequency of the fiber to be measured. The test was repeated 20 times and the average value taken.

Crimp product: The length (a) of a sample under an' initial load (2 mg. per unit denier of the sample to be measured). Then a load of 50 mg. per unit denier was applied to the sample and the length (b) after 50 seconds was measured. The crimp product was determined by the following formula:

Crimp product X Residual shrinkage (percent): A load of 300 mg. per unit denier was applied to the sample to be measured and the length (a) of the sample was measured. Then the above-mentioned sample was treated in boiling water for 10 minutes and was dried at 80 C. for 30 minutes. Then a load of 300 mg. per unit denier was applied thereto and the length (b) of the sample was measured. The residual shrinkage was determined by the following formula:

ab XIOO 7 EXAMPLE 1 A copolymer consisting of 91 parts of acrylonitrile, 9 parts of methyl acrylate and 0.5 part of sodium methallylsulfonate and a copolymer consisting of 89 parts of acrylonitrile, 11 parts of methyl acrylate and 0.5 part of sodium methallylsulfonate were separately dissolved in respective 49% aqueous solutions of sodium thiocyanate to prepare two kinds of spinning solutions. Equal amounts of them were led into a spinning apparatus mentioned in British Pat. No. 954,274 through respective metering pumps and were extruded into a coagulating bath (3 C.) consisting of 8% aqueous solution of sodium thiocyanate. In this case, a spinnerette having 6532 orifices (orifice diameter of 0.09 mm.) was used.

Then the formed composite filaments were washed with water, stretched 9 times the initial length, and then dried in high humidity air having a dry-bulb temperature of 120 C. and wet-bulb temperature of 78 C.

Then the dried composite filaments were continuously fed to the heat-relaxing treatment apparatus shown in FIG. 4 and heat-treated while in a relaxed state in saturated steam at 120 C. for 3 minutes to develop three-dimensional coil crimps. In this case, 200% water content was imparted to said filaments by making the filaments flow together with warm water on the inclined chute 22 between the inlet sealing part 12 and the conveyor 52. The filaments heat-treated in a relaxed state were then conveyed continuously to the outlet water cylinder 66 and were pulled out from the heat-relaxing treatment apparatus while maintaining the pulling-out tension according to the present invention by the tension controlling rods 58 provided in said outlet water cylinder 66. In this case, the hot water temperature in the outlet water cylinder 66 was varied to be 50, 55, 60, 70, 90 and 99 C. The filaments thus pulled out were dried with hot air at 80 C. to obtain an acrylic conjugate fiber of 3 deniers. The crimp frequency, crimp product and residual shrinkage of the resulting fibers are shown in Table 1.

Then the acrylic conjugate fibers were treated for minutes with boiling water while being kept unrestricted to develop three-dimensional coil crimps and were then dried with hot air at 70 C. The crimp frequency and crimp product of the conjugate fibers thus obtained were measured and are shown in Table l.

is 90 mg./d. However, in this example, such various pulling tensions as are shown in'T able 2 were applied.

The fibers thus led out were dried with hot air under a temperature condition of 85 C. and then its crimp frequency, crimp product and residual shrinkage were measured.

Then the conjugate fibers thus obtained were treated for 10 minutes in boiling water while being kept unrestricted to develop three-dimensional coil crimps and were then dried with hot air at 70 C. and the crimp frequency and crimp product were measured. The results were shown in followin Table 2.

TABLE 2 Before boiling After boiling Water treatment water treatment Pulling-out Crimp Crimp Residual Crimp Crimp tension freprodshrinktreprod- (mgJtL) quency uet age queney not It is apparent from the Table 2 that, in case the tension applied to the fibers in pulling out through the water column 66 is made larger than the load defined by the relative formula proposed in the present invention, the resulting fibers have a residual shrinkage.

EXAMPLE 3 Filaments spun, stretched and dried in the same manner as in Example 1 were fed to a heat-relaxing treatment apparatus as shown in FIG. 4 and were heat-treated in a relaxed state for 3 minutes in saturated steam at 115- C. to develop three-dimensional coil crimps. In this case, the filaments and warm water were made to flow concurrently between the inlet sealing part 12 and the conveyor 52 to impart water to the filaments at such rate as in Table 3. The filaments thus heat-treated in a relaxed state were led to the outlet water cylinder 66 filled with hot water at 70 C. and were pulledout through the outlet seal 14 while a pulling-out tension of 91 mg./ d. was being applied. The coil crimps of the filaments were substantially removed due to the tension of the tension controlling rods 58in the water cylinder 66.

It will be apparent from the above that, only by pulling out the filaments while satisfying both tension and heating temperature defined in the present invention, can there be produced acrylic conjugate fibers which have latent three-dimensional coil crimps, have no residual shrinkage in the subsequent heating or dyeing treatment and are excellent in the crimp developability.

EXAMPLE 2 Fibers which were obtained by being spun, stretched, dried and heat-treated in a relaxed state in the same manner as in Example 1 were led into the outlet water cylinder 66 filled with hot water at 70 C. and were pulled out from the heat-relaxing treatment apparatus while the pulling-out tension was being varied by changing the positions of the tension controlling rods 58 provided in said outlet water cylinder 66 to obtain acrylic conjugate fibers of 3 deniers having a latent crimpability. In this case, the optimum pulling-out tension to be imparted to the fibers by the tension controlling rods in the outlet water cylinder Then the obtained conjugate fibers were treated for 10 minutes in boiling water while being kept unrestricted to develop three-dimensional coil crimps and were then dried with hot air at 70 C. The obtained fiber showed such crimp frequency and crimp product as are shown in Table 3 in response to the variation of the water content given to the filaments in the relaxation heat treatment.

TABLE 3 Water content (percent) 50 200 300 Crimp frequency 10 15 19 22 23 Crimp product 10 22 30 38 40 9 EXAMPLE 4 A copolymer consisting of 94 parts of acrylonitrile, 6 parts of methyl acrylate and 0.5 part of sodium methallylsulfonate and a copolymer consisting of 91 parts of acrylonitrile, 9 parts of methyl acrylate and 0.5 part of sodium methallylsultonate were separately dissolved in respective 49% aqueous solutions of sodium thiocyanate to prepare two different kinds of spinning solutions. Using these spinning solutions, filaments were formed, stretched and dried in the same manner as in Example 1. The the dried filaments were continuously fed into a heat-relaxing treatment apparatus shown in FIG. 4 and were heat-treated in a relaxed state for 3 minutes in saturated steam at 130 C. to develop three-dimensional coil crimps. In this case, 200% water content was imparted to the filaments between the inlet sealing part 112 and the conveyer 52. The filaments thus heat-treated in a relaxed state were led to the outlet water cylinder 66 filled with water at 70 C. and were pulled out through the outlet seal 14 while a tension of 120 mg./d. was being applied to them by the tension controlling rods 58. The three-dimensional coil crimps of the thus obtained acrylic conjugate fibers had been substantially removed due to the action of the pulling-out tension by the tension controlling rods 58.

Said fibers were then passed through hot water at 75 C., were fed to a stuffing box type crimper, were treated with an oil agent, were then cut with a cutter to form staple fibers, which were then dried with a hot air (85 C.) dryer.

The resulting staple fibers had plane zigzag crimps of a crimp frequency of 11.2 and a crimp product of 8.3. Then the fibers were kept unrestricted and treated for minutes in boiling water to develop three-dimensional coil crimps. After they were dried with hot air at 70 C., a crimp frequency of 22 and a crimp product of 32 were recorded.

What is claimed is:

1. In a process for producing acrylic conjugate fibers containing at least 85% by weight of acrylonitrile and up to by weight of a monomer copolymerizable with acrylonitrile and selected from the group consisting of methyl acrylate and vinyl acetate by compositely wetspinning at least two fiber forming acrylonitrile polymers having difierent shrinking characteristics, and stretching, drying and heat-treating the spun filaments in a relaxed state, the improvement wherein (1) one of the fiber forming acrylonitrile polymers is a high shrinking acrylonitrile polymer containing from to 94% by weight of acrylonitrile and one of the fiber forming acrylonitrile polymers is a low shrinking acrylonitrile polymer containing a greater percentage amount of acrylonitrile than the high shrinking acrylonitrile polymer, (2) the heat-relaxing treatment is conducted at a temperature of IDS- C. while maintaining a moisture content in the filaments of more than by weight of the dry fiber and (3) subsequent to heat-treating the filaments in a relaxed state the filaments are pulled out of the said treatment into water having a temperature of from 60 to 99 C. while applying to the filaments a tension represented by the formula 3896 F=1.330X10- (100AN)- e T /g when 35 3g T372, or by the formula 1 L F=3.737 10- (10OAN)' e T References Cited UNITED STATES PATENTS 2/ 1971 Fujita et a1. 264-171 11/1971 Nakayama et a1. 264-171 5/1972 Lulay 264-168 FOREIGN PATENTS 8/1968 Japan 264-471 JAY H. WOO, Primary Examiner U.S. Cl. X.R. 264171, 182 

